Method for coiling a wire around a stator core

ABSTRACT

A winding of a motor is formed by coiling a wire around a slotless stator core with combination of troidal coiling and array coiling. The toroidal coiling is carried out in a manner such that the wire is coiled without any intersecting turns in one direction for the formation of the winding as it is coiled rotating spirally. By this coiling method, the accuracy of the position of the winding in the direction tangent to the surface of the stator core can be improved. The array coiling is carried out in a manner such that the winding is formed in layers that are stacked on one another. By this coiling method, the accuracy of the position of the winding in the direction normal to the surface of the stator core can be improved. Thus, the overall thickness of the winding can be made uniform.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for coiling a wire around aslotless stator core of a motor.

2. Description of the Prior Art

Components of various precision apparatuses, such as optical andelectronic apparatuses, require working accuracy of the nanometer orderto meet the requirement for the development of higher-accuracy,higher-density, and higher-integration versions. A very high resolutionis expected of a machine tool, stepper,. electron-beam exposure system,etc. that are used to work these high-precision components. In general,these machining and manufacturing apparatuses are provided with apositioning device. In many cases, the position control of thepositioning device is effected by means of a rotary servomotor or linearmotor that is controlled by means of a CNC. In order to increase theworking accuracy of the components, therefore, the rotary servomotor orlinear motor must be controlled with high accuracy.

FIG. 10 is a schematic sectional view for illustrating a magneticcircuit of a conventional servomotor. In this servomotor, slots 24 areformed in a stator core 21, which extends about a rotor 25. A winding 23formed of a coiled wire 22 is embedded in each slot 24, whereby amagnetic circuit is formed. In this magnetic circuit, lines 27 ofmagnetic force pass through tooth portions 26 between the slots 24.Thus, the lines 27 of magnetic force extend depending on the locationand shape of the tooth portions 26, and are not influenced by the way ofcoiling the winding 23.

Usually, the rotary servomotor or linear motor is subject to torqueripples, which must be minimized in order to control the motor with highaccuracy.

Torque ripples can be divided broadly into two categories; one based onstructural condition and the other based on electromagnetic condition.In the case of the rotary servomotor, for example, frictional resistanceproduced in a bearing for the shaft of a rotor can be a torque ripplebased on the structural condition. On the other hand, magnetostrictioncaused between the rotor and a stator can be a torque ripple based onthe electromagnetic condition.

Conventionally, in order to restrain the occurrence of torque ripplesbased on the structural condition, a proposal is made to reducefrictional resistance by supporting the shaft in a noncontact manner bymeans of a pneumatic or magnetic bearing. Further, use of a slotlessstator core is proposed to restrain the occurrence of torque ripplesbased on an electromagnetic condition.

In order to form a winding by coiling a wire around a stator core, ingeneral, slots are formed in the stator core. The slots may producecogging torque. In the case of the stator core having slots,electromagnetic action on the rotor depends on the slot shape, and isinfluenced little by the wire coiling mode. Accordingly, it is necessaryonly that the number of turns of the winding be equal to a set number,and the position and shape of the winding are not very importantfactors.

In the case of the motor that uses the slotless stator core, on theother hand, the positional accuracy and shape of the winding constituteessential factors that determine the electromagnetic action on therotor.

FIG. 11 is a schematic sectional view for illustrating a magneticcircuit of a slotless motor, and FIG. 12 is a schematic sectional viewfor illustrating positional errors of a winding.

As shown in FIG. 11, a winding 33 is pasted on the inner surface of aring-shaped stator core 31 of the slotless motor that is opposed to arotor 35. The stator core 31 is formed having no slots or toothportions. Since lines 37 of magnetic force are influenced by thelocation and the way of coiling of the winding 33, the positionalaccuracy of the winding 33 pasted on the stator core 31 constitutes afactor that determines the incidence of torque ripples.

As shown in FIG. 12, the positional errors of the winding include (a)misalignment between turns of the wire in each block of the winding, (b)an error in the pasting position for the wire in the circumferentialdirection of the stator core, and (c) an error in the pasting positionfor the wire in the radial direction of the stator core. In some cases,torque ripples attributable to the positional errors of the winding aregreater than in the case of a motor having slots.

A method for coiling a wire around a slotless stator core has alreadybeen proposed. FIGS. 13 and 14 are views for illustrating this coilingmethod.

As shown in FIGS. 13 and 14, windings 52 in the form of a simple segmenteach are prepared in advance by coiling a wire like an array by means ofa jig or the like. These segment-shaped windings 52 are pasted on astator core 51 and then connected to one another through a connectingwire. By doing this, the positional accuracy of the windings duringassembly can be improved.

According to this method for coiling the wire around the slotless statorcore, however, the winding is pasted on only one side of the statorcore, so that satisfactory strength cannot be obtained with ease. In thecase where the entire structure is molded, therefore, the winding maycome off as a molding agent undergoes cure shrinkage.

Since the segment-shaped windings overlap one another, moreover, theymust have a complicated three-dimensional shape. More specifically, afirst-phase winding segment 52 (e.g., segment of U-phase winding),second-phase winding segment 54 (e.g., segment of V-phase winding), andthird-phase winding segment 55 (e.g., segment of W-phase winding)overlap partially one another, and are pasted continuously on the statorcore 51 in the circumferential direction. In order to fix the height ofa straight portion (which serves as a magnet) of each segment in thenormal direction, therefore, the winding segment 52 is formed having abent portion 53.

The bent portion 53 is a portion in which the coating of the wire can bebroken most easily, and is situated corresponding to an edge portion ofthe stator core. Therefore, a short circuit between lines orline-to-ground fault easily occurs in this portion. Accordingly, thewire is subjected to a substantial bending stress, so that its coatingmay be broken, possibly causing a short circuit between lines orline-to-ground fault. Besides, it is hard to arrange the windingsegments with high positional accuracy, due to positional errorsattributable to differences in shape and size between the segments orerrors in the normal direction caused by adhesive bonding.

As shown in FIG. 15, moreover, winding lugs 58 protrude in the axialdirection of a motor shaft 56 from the stator core 51 of status 30. Thelugs 58 have no electromagnetic effect on the rotor. If the number ofturns increases, therefore, the motor size becomes larger, thusconstituting a hindrance to miniaturization. In the example shown inFIG. 16, spot-faced grooves 59 are formed by cutting those portions of ahousing 57 of a support member for the stator and the like whichcorrespond to the lugs 58, individually. If the motor is reduced in sizein this manner, its mechanical rigidity lowers inevitably.

OBJECTS AND SUMMARY OF THE INVENTION

The object of the present invention is to provide a method for coiling awire around a slotless stator core with high positional accuracy,thereby forming a winding capable of generating a uniform magneticfield.

In an aspect of the present invention, there is provided a method inwhich a winding is formed by toroidally coiling a wire like an arrayaround a slotless stator core, whereby a stator of a rotary or linearmotor is formed.

In the following explanation, "toroidal coiling" means a coiling methodcarried out in a manner such that wire is coiled without anyintersecting turns in one direction for the formation of the winding asit is coiled rotating spirally. By using this coiling method, theaccuracy of the position of the winding in the direction tangent to thesurface of the stator core can be improved.

Further, "array coiling" means a coiling method carried out in a mannersuch that winding is formed in layers that are stacked on one another.By using this coiling method, the accuracy of the position of thewinding in the direction normal to the surface of the stator core can beimproved. By improving the positional accuracy of the winding in thenormal direction, the overall thickness of the winding can be madeuniform.

Thus, the positional accuracy of the winding can be improved for boththe directions tangent and normal to the surface of the stator core bycoiling with combination of troidal coiling and array coiling. As thewinding is formed with high positional accuracy for both thesedirections, the electric resistance and inductance of the winding can bemade uniform, so that a uniform magnetic field can be formed.

In troidal coiling, if wire is coiled in layers at given pitches, thepositional accuracy of the winding can be improved for both thedirections tangent and normal to the surface of the stator core. Bydoing this, a uniform magnetic field can be formed.

In case of troidal coiling, no intersecting turns are formed in wirewithin each layer in one direction for the formation of the winding. Ifthe coiling operation is repeated so that the next layer is coiled,however, intersecting turns are formed in wire between the adjacentlayers. Those intersecting turns are situated on that side of a magneticfield generated by the stator which influences the rotation of a rotorless. Depending on the location of the intersecting turns, the influenceof the unevenness of the magnetic field generated therein on torqueripples can be lessened. For example, the intersecting turns may belocated on an end face of the stator in the axial direction thereof oron the outer peripheral surface of the stator on the side remoter fromthe rotor.

In the case where wire is toroidally coiled around a ring-shaped statorcore, gaps are formed between wire turns on the outer-diameter side dueto the difference between the inner and outer diameters of the statorcore. Normally, however, the rotor is situated on the inner-diameterside of the stator. If the magnetic field is made uneven by the gapsbetween the wire turns on the outer-diameter side, therefore, therotation of the rotor cannot be influenced thereby.

According to the invention, moreover, wire for the winding has a flatrectangular cross section, and is coiled so that the adjacent sides ofthe respective rectangular cross sections of the adjacent wire turnsextend parallel to one another. If wire is a round wire having acircular cross section, the wire turns at the return end portions of thewinding are inevitably stacked in an offset manner even in the case ofarray coiling, so that the magnetic field may become uneven. If wireaccording to the invention has a flat rectangular cross section, it canbe coiled so that the adjacent sides of the respective rectangular crosssections of the adjacent wire turns extend parallel to one another, withthe result that a uniform magnetic field can be formed even at thereturn end portions of the winding.

Further, enlargement of the size of the entire winding can be restrainedby suitably settling the ratio between the respective lengths of thelong and short sides of the rectangular cross section of the wire.

In another aspect of the invention, there is provided a coiling methodfor forming windings, in which the windings for individual phases, thenumber of which depend on the number of poles, are connectedelectrically to one another by means of wiring on a printed board thatis provided on an end face of the stator core.

According to the invention, moreover, there is provided a coiling methodfor forming windings, in which a printed board is pasted on one end faceor each of the two opposite end faces of the stator core, and the wireis coiled together with the printed board around the stator core.

In the case where a multipolar motor is designed to be driven indifferent phases, a plurality of windings are formed on its stator,corresponding to the number of poles of the motor and the number ofphases. In the case of the stator of an eight-pole three-phase ACservomotor, for example, unit windings formed by combination of troidalcoiling and array coiling, hereinafter referred to as segment, arearranged individually in 24 (=8×3) positions within an angular range of15° on a slotless stator core. In arranging the segments, each twoadjacent segments are coiled in opposite directions, and each threesegments are of the same phase.

The segments are connected by means of the printed board that is pastedon one end face or each of the two opposite end faces of the statorcore. Further, the wire is coiled around the stator core and the printedboard in a lump. This arrangement facilitates the connection of thesegments. Furthermore, the projection of lugs of the windings islessened, so that the motor can be reduced in size. Since the wire fixesthe stator core and the printed board in one united body, moreover, theresulting structure is less liable to separation or dislocation of thewire. Since each edge portion of the stator core is covered by theprinted board, furthermore, the bending stress on the wire andexfoliation of the insulating coating can be restrained. The function ofthe printed board can be improved by rounding the profile of the edgeportion of the board.

A stator of a motor to which the above-described method is appliedcomprises a ring-shaped slotless stator core having a rectangular crosssection and a plurality of winding segments formed by coiling a wirearound the stator core, the number of the segments depending on thenumber of poles of the motor and the number of phases of an AC powersource. Each of the winding segments includes at least a first windinglayer, formed by spirally coiling the wire in a first direction on thestator core lest any portion of the wire intersect any other wireportion, and a second winding layer, formed by spirally coiling the wirein a second direction opposite to the first direction on the firstwinding layer lest any portion of the wire intersect any other wireportion, and a second winding layer, the second winding layer beingstacked on the first winding layer. Moreover, the winding segments havethe same number of turns and external shape and are arranged on thestator core at equal spaces in the circumferential direction.

Further, the wire that constitutes the winding segments has a circularor flat rectangular cross section.

Further, each of the winding segments is formed by coiling the wirearound the stator core and a printed board pasted on at least one endface of the stator core.

Furthermore, the winding segments are connected to one another by meansof a printed pattern on the printed board pasted on at least one endface of the stator core.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects and features of the invention willbecome apparent from the following description of preferred embodimentsof the invention with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view taken from the side of a rotor, showing awinding formed by a wire coiling method according to the inventionapplied to a stator of a three-phase AC servomotor;

FIG. 2 is a plan view of the stator of FIG. 1 taken from the rotor side;

FIG. 3 is a sectional view taken along line A--A of FIG. 2, showing awire having a circular cross section;

FIG. 4 is a sectional view taken along line A--A of FIG. 2, showing awire having a flat rectangular cross section;

FIG. 5 is a perspective view taken from the side remoter from the rotor,showing a winding formed by the wire coiling method of the inventionapplied to a stator of a three-phase AC servomotor;

FIG. 6 is a plan view of the stator of FIG. 5 taken from the rotor side;

FIG. 7 is a sectional view taken along line B--B of FIG. 6, showing awire having a circular cross section;

FIG. 8 is a sectional view taken along line B--B of FIG. 6, showing awire having a flat rectangular cross section;

FIG. 9 is a sectional view of the three-phase AC servomotor using thestator shown in FIG. 1 or 5;

FIG. 10 is a schematic sectional view for illustrating a magneticcircuit of a conventional servomotor;

FIG. 11 is a schematic sectional view for illustrating a magneticcircuit of a conventional slotless motor;

FIG. 12 is a view for illustrating positional errors of a winding;

FIG. 13 is a view for illustrating a prior art example formed by coilinga wire around a slotless stator core;

FIG. 14 is a view for illustrating the way the wire of FIG. 13 isattached to a slotless stator core for a three-phase motor;

FIG. 15 is a sectional view of the three-phase motor using the slotlessstator core of FIG. 14; and

FIG. 16 is a view showing spot-faced grooves formed in a housing andindividually storing lugs of a winding.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the accompanying drawings of FIGS. 1 to 9, there willbe described a case in which a coiling method of the present inventionis applied to a stator 1 of a three-phase AC servomotor.

Printed boards 12 and 13 are put intimately on the opposite end faces(upper and lower end faces in FIG. 1), individually, of a stator core 11in the axial direction of a motor shaft. A wire 2, having a first end 4and a second end 5, is coiled around the printed boards 12 and 13 andthe stator core 11 so as to enclose them integrally. This way of wirecoiling is combination of toroidal coiling and array coiling to form awinding segments 3. FIG. 1 illustrates three winding segments 3 with agap 6 between the segments.

In toroidally coiling the wire 2 around the stator core 11 and theprinted boards 12 and 13, the wire 2 is turned spirally in thelongitudinal direction (direction A--A of FIG. 2) of the stator core 11.For each layer of a winding to be formed by the coiling operation, thewire 2 is toroidally coiled without any intersection produced, as shownin FIG. 2.

After the wire 2 is coiled for one layer in the longitudinal directionof the stator core 11 around the core 11 and the printed boards 12 and13, it is turned back at an end portion and coiled superposed on thelayer (first layer) that is formed in the previous cycle of coilingoperation. For the next layer (second layer), the wire 2 is coiledtoroidally as in the case of the first layer.

By this operation, the winding is formed in layers, and the individuallayers are stacked for array coiling.

FIGS. 3 and 4 are views for illustrating this array coiling. FIG. 3shows the case of a wire having a circular cross section, while FIG. 4shows the case of a wire having a flat rectangular cross section.

As shown in FIG. 3, a wire 2a is toroidally coiled for each of layers,and the individual layers are stacked by array coiling. One circularcross section of the wire 2a in each layer is located over the boundarybetween the respective circular cross sections of two adjacent turns ofthe wire 2a in each underlying layer.

As shown in FIG. 4, on the other hand, a wire 2b is toroidally coiledfor each of layers, and the individual layers are stacked by arraycoiling. One rectangular cross section of the wire 2b in each layer isput directly on the rectangular cross section of the wire 2b in eachdirectly underlying layer. If the wire 2b is coiled so that the shortside of the rectangular cross section of each turn of the wire 2b isparallel to that of its adjacent turn in each layer, as shown in FIG. 4,the respective end portions of turned edges of the wire 2b in each layerare trued up, so that a uniform magnetic field can be formed.

Further, enlargement of the size of the entire winding can be restrainedby suitably settling the ratio between the respective lengths of thelong and short sides of the rectangular cross section of the wire 2b.For example, the overall thickness of the motor in the radial directionfrom the axis of the motor shaft can be reduced by stacking therectangular wire 2b in layers so that the short side of each rectangularcross section is in line with the radial direction.

When the wire advances in one direction as any one layer is coiledtoroidally, each two adjacent turns of the wire never intersect eachother, as mentioned before. When the next layer starts to be coiledafter coiling the first layer is finished, however, some turns of thetwo layers intersect one another. Those intersecting turns are situatedon that side of a magnetic field generated by the stator whichinfluences the rotation of a rotor less, that is, on the side remoterfrom the rotor in the example shown in FIG. 5. Alternatively, theintersecting turns may be situated on the end-face side of the stator inthe axial direction of the motor shaft.

FIG. 6 is a view of the stator taken from the rotor side, showing theintersecting turns between the adjacent layers. As seen from FIG. 6, theangle of inclination of the winding to the longitudinal direction of thestator core (direction B--B of FIG. 6) varies between the layers. Thewire can be coiled in this manner by array coiling shown in thesectional view of FIG. 7 or 8.

As shown in FIG. 7 or 8, a wire 2a or 2b is toroidally coiled for eachlayer, and the individual layers are stacked by array coiling. Acircular or rectangular cross section of the wire 2a or 2b in each layeris put directly on the circular or rectangular cross section of the wire2a or 2b in each directly underlying layer.

As shown in FIG. 9, the rotor 15 is rotated by means of electromagneticforce that is generated between lines of magnetic force therefrom andcurrent that flows through the toroidal coil. The lines of magneticforce that are generated by a magnet in a rotor core cross the toroidalcoil on the rotor side, pass through the stator core, cross the toroidalcoil again, and return to the rotor, thereby forming a magnetic circuit.When current flows through the toroidal coil that are crossed by thelines of magnetic force, electromagnetic force is produced, so that thestator is subjected to force. Since the stator is fixed, the rotor isrotated by means of a reaction force to counter this force.

According to the coiling method of the present invention describedabove, lugs that are formed on conventional windings need not be formed,so that the axial length of the motor shaft 16 can be restricted, thusensuring miniaturization. As shown in FIG. 9, moreover, a windingsegment 3 can be stored in a motor 10 without forming a spot-facedgroove in a housing 17.

Although the case of a rotary servomotor 10 has been described inconnection with foregoing embodiment, the present invention may be alsoapplied to a linear motor.

According to the present invention, as described herein, there may beprovided a winding of a slotless stator core capable of generating auniform magnetic field and a wire coiling method for the winding.Further, there may be provided a winding of a slotless stator corearranged with high positional accuracy and a wire coiling method for thewinding. Furthermore, there may be provided a winding of a slotlessstator core having less projection from the stator core in the axialdirection of a motor and a wire coiling method for the winding.

What is claimed is:
 1. A method for coiling a winding around a slotlessstator core, comprising:coiling a first layer of turns of a wire aroundthe slotless stator core such that as the wire advances in a firstdirection no portion of the coiled wire intersects any other wireportion coiled previously; and return coiling the wire in a second layerof the wire turns around the first layer such that as the wire advancesin a second direction opposite to the first direction no portion of thesecond layer of coiled wire intersects any other previously coiled wireportion of the second layer.
 2. A method for coiling a winding around aslotless stator core according to claim 1, further comprising pasting aprinted circuit board on at lease one end face of the slotless statorcore prior to coiling the first layer of turns of the wire, and coilingsaid wire around the stator core and the printed circuit board.
 3. Amethod for coiling a winding around a slotless core according to claim1, further comprising positioning intersecting wire turns producedbetween the layers when the wire is returned after being coiled for onelayer and is further coiled for another layer, on a side of the slotlessstator core opposite from a rotor on which said slotless stator core maybe positioned.
 4. A method for coiling a winding around a slotless coreaccording to claim 1, further comprising positioning intersecting wireturns produced between the layers when the wire is returned after beingcoiled for one layer and is further coiled for another layer, on anend-face side of the slotless stator core in an axial direction of amotor shaft.
 5. A method for coiling a winding around a slotless coreaccording to claim 1, wherein said wire coiled around the slotlessstator core has a circular cross section.
 6. A method for coiling awinding around a slotless core according to claim 1, wherein said wirecoiled around the slotless stator core has a flat rectangular crosssection.
 7. A method for coiling a wire around a slotless stator core,comprising:forming a slotless stator core to be positioned in a motor;coiling a first layer of wire around the slotless stator core such thatas the wire advances in a first direction no portion of the coiled wireintersects any other wire portion previously coiled; and coiling asecond layer of the wire around the first layer such that as the wireadvances in a second direction opposite to the first direction, noportion of the second layer of coiled wire intersects any otherpreviously coiled wire portion of the second layer.
 8. A method forcoiling a wire according to claim 7, further comprising placing anelectrically conductive medium on an end face of the slotless statorcore prior to coiling the first layer of wire around the slotlessstator.
 9. A method for generating a uniform magnetic field in a motorhaving a slotless stator core, comprising:toroidially coiling a wirearound said slotless stator core in a first direction along alongitudinal axis of the slotless stator core; toroidially coiling saidwire around said slotless stator core in a second direction oppositesaid first direction, along said longitudinal axis of said slotlessstator core; and forming a plurality of wire layers around said slotlessstator core by said toroidial coiling such that said plurality of wirelayers are positioned relative to one another so as to reduce a magneticfield non-uniformity effects.
 10. A method for improving magnetic fielduniformity according to claim 9, further comprising placing anelectrically conductive medium on an end face of the slotless statorcore prior to toroidally coiling the wire around the slotless statorcore in the first direction along the longitudinal axis of the slotlessstator core.
 11. A method for improving magnetic field uniformityaccording to claim 9, wherein the magnetic field non-uniformity effectsinclude effects due to torque ripples.